The present disclosure relates to indicator devices for determining the ageing of articles (e.g., plastic articles), which are degradable by ultraviolet (UV) radiation.
Plastic is a material that can be used in many contexts. For example, plastic is employed in the manufacture of different consumer related products. More particularly, since plastic withstands impact and is readily/cost effectively formed into different shapes, plastic is suited for use in safety and personal protection articles (e.g., helmets (e.g., construction helmets, bike helmets, ski helmets, and the like), car and bicycle seats for children, and the like).
One drawback of plastic is that it degrades under the action of UV radiation. For example, the presence of UV radiation leads to cracks in plastics of all different types. Further, it is noted that degradation of the plastic article in the absence of UV radiation can be minimal (e.g., when the plastic article is packed and stored in boxes/containers). Differences in the speed of ageing are also observed depending on whether the plastic article is used indoors or outdoors and whether the plastic article is used in northerly or southerly latitudes. In other words, the UV radiation exposure of the plastic article can be a decisive factor in the speed of aging of the plastic article.
Referring to FIG. 1, a graphical representation of generalized isolines of global radiation is illustrated. The global UV radiation per year is measured according to ASTM D1435. The intensity of UV radiation illustrated in FIG. 1 is measured in kLy (kilo-Langley), which represents how much UV radiation energy falls on a centimeter square area (cm2) per year. FIG. 1 illustrates that the intensity of UV radiation varies depending on geographical location. For example, the intensity of UV radiation is more intense in the deserts of Africa compared to a city in Western Europe. As such, the useful lifetime of a plastic article varies depending on the geographical location of its use, since some areas receive a greater intensity of UV radiation than other areas.
Presently, a “date marking” is disposed on a plastic article to provide a consumer with an estimated lifetime of the article. When a date marking is employed, considerable safety margins are employed in order to be certain that an aged article whose mechanical strength is defective is no longer used. For example, the date marking is set based on an assumed time limit for the product to reach maximum UV exposure. As such, this date marking might not adequately reflect the useful life of the article (e.g., in the above example, a plastic article ages faster than the date marking in some areas, particularly in the deserts of Africa). Further, date marking can, in many cases, lead to usable articles, which have not been exposed to UV radiation and have not aged, becoming unsellable when their date marking has expired. However, in order to avoid injury to a person or damage to property, the date marking is honored. By erring on the side of caution by respecting the date marking, considerable economic losses are suffered by manufactures, retailers, end-users, and the like, who might have stored large quantities of the dated marked articles.
Further, a time period for use of an article can be set by mandate, for example, by a legislative restriction set by a given country, which can differ from country to country. Again, the actual durability (lifetime) of a plastic article can exceed a given time period set by a legislature. As such, removing an article from use prematurely (i.e., before its useful life has expired) can further cause economic losses to be suffered, since the article would be replaced more frequently compared to replacing the article when its useful lifetime has expired.
Accordingly, what is needed in the art are indicator devices that can measure the ageing of articles that degrade with UV radiation exposure.